My mechanic said that the tensioner rails should be replaced every 100K. He said that there is no way to tell when they are getting old and brittle (since they are plastic). If you purchased a used vehicle and there is no records that they have been replaced then you are better off to have them replaced to save you the $$ that it is gonna cost you to have it fixed along with the valve job it will need.

Guess the ol' saying of "an ounce of prevention...." is true (at least in the case of MB maintnenaince).

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Frank
84 500SEL EURO 101K ( JUST LIKE MY 1ST WIFE. GLAD TO GET RID OF HER! )
85 300D 310K (sold)
90 350SDL 184K sold
83 300D 118K (sold)
88 300E 153k (sold)
93 400E 105K (sold)